Characterization of poly(vinyl alcohol) hydrogel for prosthetic intervertebral disc nucleus

In the recent years, development of intervertebral disc prosthesis has been of great concern to the world of medicine and science. Substitution of the spinal disc or its part being displaced or damaged due to trauma or a disease process for the artificial structure well imitating high tensile properties and elasticity of the real disc would highly improve the existing treatment techniques. In this work, the attempt to develop the PVA-based hydrogel material for artificial spinal disc has been made. The polymer was initially processed with the use of formaldehyde solution as a crosslinking agent and sulfuric acid as a catalyst. Then properties of the material have been altered by saturating the already existing PVA hydrogel with a mixture of hydrophilic and hydrophobic monomers (2-hydroxyethyl methacrylate and methyl methacrylate) and a subsequent exposure to ionizing radiation (⁶⁰Co source). In this way, interpenetrating polymer network has been built on the crosslinked PVA scaffold. Resulting structures were tested for their mechanical behavior at different loads. Series of measurements leading to the determination of the physicochemical properties of created gels including crosslink density and swelling abilities were also performed.     

Mesolytic Scission of C-C Bonds as a Probe for Photoinduced Electron Transfer Reactions of Quinones

Photoinduced electron transfer reactions of chlorinated benzoquinones are investigated using bibenzylic donors that undergo rapid fragmentation upon oxidation. The fragmentation rates and the quantum yields are used to probe the dynamics of back-electron transfer (BET) in two types of radical ion pairs. The triplet ion pairs formed by interception of excited state quinones give products with high quantum yields. The singlet ion pairs formed by irradiation of the charge-transfer (CT) complexes between the quinones and the donors undergo reactions with significantly lower efficiency. The advantage of the first method (triplet quenching) over the CT-irradiation depends on the energetics of BET. It is large for reactions with relatively small DeltaG(et) for BET and it decreases for reactions with more negative DeltaG(bet). The indirectly obtained rates of BET are in excellent agreement with literature data for similar, but unreactive systems, and the rates of C-C bond scission in radical cations generated in these systems are consistent with the thermodynamics of these processes.     

Synthesis and Crystal Structure of Europium(II) Tartrate Tetrahydrate, [Eu(C4H4O6)(H2O)2](H2O)2

Single crystals of [Eu(C₄H₄O₆)(H₂O)₂](H₂O)₂ were obtained from the combination of solutions of EuCl₂, previously obtained by electrolysis of an aqueous solution of EuCl₃, and tartraric acid, neutralized by LiOH. The crystal structure (orthorhombic, P2₁2₁2₁, Z = 4, a = 948.9(1), b = 954.6(1), c = 1098.4(1) pm; R(F) = 0.0242 and R_w(F²) = 0.0585 for I > 2σ(I); R(F) = 0.0256 and R_w(F²) = 0.0592 for all data) is isotypic with [Ca(C₄H₄O₆)(H₂O)₂](H₂O)₂ and [Sr(C₄H₄O₆)(H₂O)₂](H₂O)₂ exhibiting a three‐dimensional structure. The divalent cations (Eu²⁺, Ca²⁺, Sr²⁺) are eight‐coordinate by oxygen atoms that originate from carboxylate and hydroxyl groups of the tartraric dianion and two of the four water molecules.     

Approaches to the enantioselective synthesis of ferrugine and its analogues

A four-step synthetic route, to ferrugine (2α-benzoyltropane), its methyl analogue (2-acetyltropane) and their N-benzyl analogues is reported. The reaction sequence uses tropinone or N-benzylnortropinone aldols as key intermediates. Reduction of aldol derived N-tosylhydrazones and oxidation of the side chain hydroxyl group followed by spontaneous diastereomer equilibration provides the final products. Relative configuration of the exo,anti N-methyl and N-benzyl aldols was retained during N-tosylhydrazone formation. The relative stereochemistry of N-tosylhydrazones was assigned by single crystal diffraction. The final products, ferrugine and its methyl analogue, were synthesized in enantiomerically pure form via asymmetric deprotonation of tropinone using chiral lithium amide/lithium chloride aggregate prepared in situ from (S,S)-N,N-bis(1-phenylethyl)amine hydrochloride.     

Linear and nonlinear optical studies in photonic crystal alloys

We report on linear transmittance and reflectance as well as on third-harmonic generation in photonic crystal alloys formed by various compositions of polystyrene and poly (methyl methacrylate) colloidal spheres of the same size. These photonic crystal alloys are structurally ordered but contain refractive-index disorder and thus provide a random variation of scattering potential. The stopgap shows a monotonic shift in wavelength as a function of composition that can be fitted by assuming an effective dielectric constant for the colloidal spheres. In each alloy a dramatic enhancement of third-harmonic generation is observed, always on the short-wavelength side of the stopgap.